Modern airplane seats, and, in particular, seats in the premium sections of a passenger airplane such as first class, are powered by actuators that enable portions of the seat to be selectively adjustable between a number of seating positions. The range of these positions may vary. For example, some powered seats may be adjustable between an upright position and a reclined position, while other seats can recline to a substantially flat position in order to function as a bed. Additionally, some airplane seats have a head rest and a foot rest that can be separately adjusted to provide a comfortable seating position. The various adjustable features of the seat are accessible and controllable using a passenger control unit, some of which may include a touchscreen or a keyboard with a display.
In use and given the confined space within an aircraft, there can be the possibility of objects, e.g., carry-on luggage items, being pinched between at least one moving section of the powered seat and an adjacent section of the seat, a bulkhead, privacy screen, or other immovable object. Such a pinch event is referred to herein as an “obstruction,” and the areas in which obstructions can occur are referred to as “pinch points.” Obstructions can result in damage to pinched objects. There is, therefore, a need for techniques to mitigate or avoid damage or injury resulting from obstructions.
Various attempts have previously been made to address the detection of potential obstructions in powered aircraft seats. For example, DE102004037913A1 by Baumann describes foil sensors arranged on the seat in and around pinch points. When an obstruction is detected, e.g., by sensing pressure exerted on the foil sensors by the pinched object, a control system can stop, start, or retract seat components in order to relieve the obstruction. However, this system requires the incorporation of additional sensors, which add weight and potential failure modes. Particularly for aviation uses, extra weight is undesirable.
GB2497332 by Jerrett describes measuring a current drawn by a seat actuator to determine when an obstruction has occurred. This scheme uses the position of the output shaft of the actuator to determine a threshold at which it will be determined that an obstruction is present.
It has been determined that the load on a seat, e.g., the weight of a passenger, can have a significant effect on the actuator current required to move components of an aircraft seat. In a example, to recline a tested seatback against the spring urging that seatback upright, a current of ˜1 A was required if the seat was empty (more current than to move the seat upright), but a current of only ˜400 mA was required if the seat was holding a 250 lb. passenger leaning against the seat back (less current than to move the seat upright). This difference can confound schemes such as those noted above that simply use actuator current to detect obstructions. Moreover, significant variations in passenger weight are not uncommon. The FAA standard average passenger weights set forth in Advisory Circular (AC) 120-27E, Jun. 10, 2005, range between 82 lb for a child in summer and 205 lb for a male adult in winter. Moreover, unoccupied seats being moved automatically or by cabin personnel can participate in obstructions with respect to nearby bulkheads or seats.
This difference is especially significant because many mechanical designs of powered seat actuators are nonlinear in behavior over their range of motion. The loads on such designs change dynamically in both position and direction as the actuators traverse. Various prior schemes are not capable of taking such nonlinear behavior into account.
U.S. Pat. No. 6,949,904 to Rumney attempts to determine whether a seat is occupied using current data, and to and adjust actuator force accordingly. However, Rumney does not describe detection of obstructions. There is, therefore, a continuing need for a way of detecting obstructions even in the face of variation in the load placed on a seat, e.g., by a passenger sitting therein.